In air conditioning apparatus equipped with devices such as outdoor fans and compressors, many motors are used as power sources for these devices, and the motors are driven and controlled by motor drive control devices.
In recent years, from the standpoint of cost reduction, a motor drive control device that uses a rotor position sensorless control scheme to drive the motor has often been used. However, with the rotor position sensorless control scheme, it is impossible to detect the position of the rotor in an uncontrolled state, which is just before startup of the motor.
Particularly in a case where the motor is used as a drive source for an outdoor fan, when an external force resulting from the effect of wind, for example, acts on the outdoor fan even though the motor is not yet being driven, the motor also rotates. If the motor is started up in this state, there is the concern that problems will occur in the motor, such as motor current which, compared to a case where the motor normally starts up in a state in which no external force is acting on the outdoor fan like in the absence of wind, is large flowing or an overvoltage occurring due to a regenerative action. Consequently, the startup stability of the motor is compromised.
In order to address this issue, a technology is known which, as described in JP-A No. 2005-137106 for example, detects the phase of the rotor from an inductive voltage generated in the motor at the time when the output of a drive voltage from an inverter to the motor has stopped. In patent document 1, the motor is started up in accordance with the phase of the rotor that has been detected.